System and method for reducing pulsatile pressure

ABSTRACT

A device for reducing pressure within a lumen includes a reservoir structured for holding a fluid therein, an injection port in fluid communication with the reservoir, a compliant body structured to expand and contract upon changes in pressure, and a conduit extending between and fluidly coupling the reservoir and the compliant body. The fluid may be a compressible or a noncompressible fluid.

FIELD OF THE INVENTION

The invention relates generally to a system and method for reducingpulsatile pressure, and more particularly to a device having a compliantbody that is implantable in a vessel for reducing pulsatile load in thevessel and a method of delivering the device.

BACKGROUND OF THE INVENTION

In patients with pulmonary arterial hypertension, a known or unknowndisease process results in vasoconstriction and proliferation of thecells making up the wall of the small pulmonary arteries. This leads toincreased resistance to blood flow and increased steady state pressurein the pulmonary artery. Over time, the increased pressure in thepulmonary artery, as well as other disease processes, cause thepulmonary artery to lose its elasticity, resulting in a decrease invascular compliance. Vascular compliance is a measure of the elasticproperties of a vessel and is defined as the change in volume in avessel in response to a change in pressure (ΔV/ΔP). A compliant vesselis able to accommodate a relatively large volume change for a givenchange in pressure. With each stroke of the heart, a volume of blood(stroke volume) is pumped from the right ventricle into the pulmonaryartery. When the compliance is low, as occurs in pulmonary arterialhypertension, the right ventricle must produce a high pressure in orderto pump each stroke volume into the pulmonary artery because the vesselis unable to stretch to accommodate the incoming blood. This results ina high pulse pressure, which is the arithmetic difference between thesystolic and diastolic pressures.

The abnormally high stiffness of the arterial wall also affects thepulse wave velocity (PWV) so that reflected waves may contributesignificantly to pulse pressure. PWV may be estimated by theMoens-Korteweg equation: PWV=(E h/2Rρ)_(1/2). An important component ofthis equation is E or Young's modulus, a measure of stiffness of thearterial wall. In pulmonary arterial hypertension, Young's modulus maybe greater than normal, resulting in a higher than normal PWV. With eachheartbeat and ejection of blood, a temporary and localized increase inhydraulic pressure is created in the pulmonary artery. This pressureimpulse propagates away from the heart as an acoustic wave. When thewave encounters an impedance discontinuity, such as an abrupt change indiameter or a branch, a reflection occurs. These reflections travelretrograde towards the heart. In a person with normal vascular stiffnessand PWV, the major reflected wave reaches the heart after the ejectionof blood. But with aging and the development of systemic hypertension,pulmonary arterial hypertension, arteriosclerosis, as well as otherconditions, vascular stiffness and PWV may be increased, causing themajor reflected wave to arrive at the heart earlier. In many patientswith pulmonary arterial hypertension, the major wave can arrive duringejection, significantly contributing to the pulmonary artery pulsepressure and cardiac work.

In 1983, Sunagawa employed the concept of elastance as a change inpressure over change in volume (elastance is ΔP/ΔV, the reciprocal ofcompliance). (Sunagawa at al., Am J Physiol Heart CircPhysiol 245:H773-H780, 1983.) In normal, healthy individuals, the elastance of thepulmonary artery and the right ventricle are matched or coupled. Muchlike impedance matching in an electrical circuit, coupling represents astate of optimum stroke work and energetic efficiency. (Borlaug et al.,Heart Fail Clin 4: 23-36, 2008.) The optimum value of the ratio ofelastance of the right ventricle to the elastance of the pulmonaryartery is between 1 and 2. (Naeitje at al., Bur Heart JournalSupplements (2007) 9 (supplement H), H5-H9.) In advanced stages ofpulmonary arterial hypertension, this ratio is decreased, a conditiontermed afterload mismatch. (Borlaug, Ventricular-Vascular Interaction inHeart Failure, Heart Failure Clin 4 (2008) 23-36.) This decouplingindicates that additional energy is needed in order to maintain flow,thus imposing additional load on the right ventricle.

Thus, as appreciated by those of ordinary skill in the art, therelatively low compliance (or high stiffness) of the pulmonary artery inpatients with pulmonary arterial hypertension leads to increased pulsepressure. It also leads to higher PWV, which causes reflected waves tocontribute to afterload, further increasing pulse pressure. Furthermore,elastance decoupling leads to a state of energetic inefficiency andincreased workload for the heart. These components combine to contributeto pulsatile load and increase the workload on the right ventricle.

In pulmonary arterial hypertension, the total load that the rightventricle must overcome to pump blood can be considered the sum of thesteady state load (due to restriction of flow caused by small vesselconstriction) and the pulsatile load (which is caused by decreasedcompliance or increased stiffness). While in the past most researchersand physicians focused on addressing the steady state load, manyresearchers now feel that pulsatile load may be of comparable importancein imposing a load on the heart.

In a normal, healthy individual, the pulmonary circulation operates at asubstantially lower pressure than the systemic circulation. The pressurein the right ventricle is usually one-sixth of that in the leftventricle. In comparison to the left ventricle, the right ventricle isless capable of withstanding chronically elevated pressures andworkloads. Initially, when exposed to high pressure the right ventricleadapts to the higher load via multiple mechanisms including hypertrophy,but as the pressure continues to rise, the heart loses this ability tocompensate, eventually leading to right heart failure, a leading causeof death in pulmonary arterial hypertension.

Drugs are the mainstay of current therapy for pulmonary arterialhypertension. An important function of the pulmonary arterialhypertension-specific drugs is to dilate the small pulmonary arteries.These medications tend to lower the steady state load by increasing thecross-sectional area of the constricted vessels, but do not directlytarget the elevated pulsatile load caused by lack of compliance.

To summarize, many pulmonary arterial hypertension patients die of rightheart failure due to chronically elevated load on the right ventricle.Increased pulsatile load is a significant component of the total loadand is caused by a relative lack of compliance in the pulmonary artery.Current therapy is not directed at improving compliance. Thus, there isa need for a solution to lower pulsatile load by increasing complianceof the pulmonary artery.

BRIEF SUMMARY OF THE INVENTION

The invention addresses the foregoing problems by providing a device forreducing pulsatile load in an artery that includes a reservoir, aninjection port, a transvascular conduit, and a compliant body. Theinternal cavities of the components are fluidly coupled to one another,allowing gas to move and pressure to equalize between the components.The reservoir may be located under the skin in the area of thesubclavian vein or in another suitable location remote to the compliantbody. The injection port, which allows for filling and pressureadjustments of the reservoir, may either be attached to the reservoir byan extravascular conduit or mounted directly to the reservoir body. Thetranavascular conduit passes through the subclavian vein, superior venacava, right atrium, and right ventricle and connects the reservoir tothe compliant body. The compliant body may be located in the pulmonaryartery and consists of a flexible membrane surrounding a compressible ornoncompressible gas or other suitable fluid.

Implantation of the device may be performed by means of a minimallyinvasive procedure using local anesthesia and fluoroscopy. For example,a first incision may be made in the subclavicular skin and a secondincision or window may be made in the subclavian vein. A pocket may beformed in the subcutaneous space adjacent to the first incision that issized for placement of the reservoir. The distal end of the compliantbody may be inserted into the subclavian vein incision with the devicedeflated. The compliant body and conduit may then be advanced until thecompliant body reaches the desired resting position in the pulmonaryartery. Although not necessary, a sheath and/or a wire may be used toguide the device into place within the vasculature. Once the compliantbody is properly situated within the pulmonary artery, the reservoir maybe placed in the subcutaneous pocket and the incision closed. As will beappreciated by those of ordinary skill in the art, the compressible gasmay be injected into the reservoir through the injection port eitherbefore or after the incision is closed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a first exemplary embodiment of apressure reducing device in accordance with the invention.

FIGS. 2A and 2B are diagrams illustrating the mechanical basis for theoperation of the invention.

FIG. 3 is a diagram illustrating exemplary cross-sectional geometries ofa compliant body in accordance with the invention.

FIG. 4 is a diagram illustrating a “bench top” pulmonary circulationtest apparatus used to simulate the operation of the pulmonaryvasculature and test various pressure reducing devices in accordancewith the invention to verify their operability.

FIG. 5 is a graph illustrating the exemplary effect that the pressurereducing device of the invention has on peak pressure.

FIGS. 6A and 6B are diagrams illustrating a first alternative embodimentof a pressure reducing device in accordance with the invention.

FIG. 7 is a diagram illustrating a second alternative embodiment of apressure reducing device in accordance with the invention.

FIG. 8 is a flowchart diagram illustrating exemplary but non-limitingtherapeutic pathways associated with the pressure reducing device of theinvention.

FIGS. 9A and 9B are diagrams illustrating exemplary cross-sectionalgeometries of a compliant body with multiple chambers.

FIGS. 10A to 10B are diagrams illustrating exemplary anchoring devicesand methods.

FIGS. 11A to 11C are diagrams illustrating exemplary anchoring devicesand methods.

FIGS. 12A and 12B are diagrams illustrating an exemplary device for usein the method in accordance with the invention.

FIG. 13 is a diagram illustrating multiple fluidly independent lumens inthe transvascular conduit in accordance with the invention.

FIGS. 14A and 14B are diagrams illustrating exemplary devices inaccordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

Generally speaking, the invention is directed to the treatment ofpulmonary arterial hypertension by improving compliance of the pulmonaryvasculature. In one exemplary embodiment, a gas-filled compliant body ispositioned in the pulmonary artery. Mimicking how a normal pulmonaryarterial vasculature stretches to accommodate each stroke volume, thegas in the compliant body compresses to accommodate this volume. Byadding a compliant body to the pulmonary artery, the system is able toaccept blood volume without causing a large change in pressure, i.e. thecompliance or ΔV/ΔP is increased. One embodiment comprises a compliantbody attached to a reservoir by means of a hollow conduit. The reservoiris, in turn, connected to a filling or injection port by means of anextravascular conduit. In this configuration, the various components arefluidly coupled with one another such that gas can flow and/or pressurecan equalize between all the components.

The device of the invention is operable to decrease peak pressure in thepulmonary artery with minimal change in mean pressure. The putativemechanisms of peak pressure reduction are achieved directly throughincreased compliance and indirectly by slowing the PWV thereby reducingthe contributions from reflected waves. As appreciated by those ofordinary skill in the art, lowering peak pressure decreases thepathologic toll on the right ventricle by reducing peak rightventricular wall stress and mechanical work. In addition, by increasingcompliance (i.e. decreasing elastance), the device improves theelastance coupling of the pulmonary artery and right ventricle, thusrepresenting a state of increased energetic efficiency. In addition,reducing peak pressure may help slow the progression of the disease inthe small arteries by reducing strain on the calcium channels andlowering the stimulus for pathologic remodeling. In total, thesebenefits result in decreased workload on the heart and improved qualityand duration of life for patients suffering from pulmonary arterialhypertension.

FIG. 1 is a diagram illustrating a first exemplary embodiment of apressure reducing device 10 in accordance with the invention. Asillustrated in FIG. 1, the device 10 generally includes a compliant body12, a reservoir 14, an injection port 16, a transvascular conduit 18extending between the compliant body 12 and the reservoir 14, and anextravascular conduit 20 extending between the reservoir 14 and theinjection port 16. The internal cavities of the foregoing components are“continuous,” thereby allowing gas to move and pressure to equalizebetween the components.

More particularly, in the exemplary implantation position illustrated inFIG. 1, the reservoir 14 is located in the subcutaneous space near thesubclavian vein while the compliant body 12 is located in the pulmonaryartery. The injection port 16 is attached to the reservoir 14 by meansof the extravascular conduit 20 and allows for gas filling and pressureadjustments of the reservoir 14 and compliant body 12. The transvascularconduit 18 connects an internal cavity of the reservoir 14 to aninternal cavity of the compliant body 12, and may pass though the heartmuch like the leads of a pacemaker.

Although the device 10 may be implanted within a patient in any suitablemanner, one exemplary method of implantation is performed by a minimallyinvasive procedure using local anesthesia and fluoroscopy. In this typeof procedure, an incision may first be made in the subclavicular skinand a pocket formed in the subcutaneous space. Then, an incision may bemade in the subclavian vein. Upon forming the first and secondincisions, a distal end of the compliant body 12 may be inserted intothe subclavian vein incision with the body deflated or inflated. Thecompliant body 12 and transvascular conduit 18 may then be advanceduntil the compliant body 12 reaches the desired resting position in thepulmonary artery. As will be appreciated by those of ordinary skill inthe art, a sheath or a wire may be used to guide the compliant body 12and transvascular conduit 18 into place. With the compliant body 12positioned in the desired resting position, the reservoir 14 may then beplaced in the subcutaneous pocket and the incisions closed. Gas may thenbe injected into the injection port 16 to fill the device.Alternatively, the device may be filled with gas prior to closing theincision in the subclavicular skin. Alternatively, part of the device 10may be filled with a liquid which has a vapor pressure of approximatelyI atmosphere at body temperature. As the gas diffuses through the wallsof the device 10 the decrease in vapor pressure allows more toevaporate.

To limit the movement of the compliant body 12 when placed in thepulmonary artery, it may be beneficial to include an anchoringmechanism. As will be appreciated by those of ordinary skill in the art,this may be accomplished in a variety of ways, as illustrated in FIGS.10A to 10B. Spring loaded anchoring members 100 may lay near thelongitudinal axis when the compliant body is deflated then protruderadially to make contact with the innermost layer of the pulmonaryartery when the complaint body is inflated. The anchoring members mayprotrude through the membrane when inflated then retract when deflated,as shown in FIG. 10B. The anchoring members may be mounted on thesurface of the membrane FIG. 10A. When-released during inflation of thecompliant body, they spring out to contact the walls of the artery.Subsequent deflation of the compliant body will retract them.

Alternately the members 100 may be compressed by a sheath 101 thatencases the compliant body 12 and transvascular conduit 18 during theimplant procedure, as shown in FIG. 10C. Removal of the sheath allowsthe members to spring out and contact the walls of the arteries.Re-introduction of the sheath retracts the members.

Alternately the anchoring mechanism may be separate from the compliantbody and may consist of anchoring members 100 on the and of a guide wire110 that pass out of the vasculature with the transvascular conduit 18as shown in FIG. 11A to 11C. The compliant body 12 and conduit 18 may bedesigned with a lumen 111 that is continuous and isolated from thedevice lumen. Such a lumen would allow the device to be passed over theguide wire 110 until the body 12 and conduit 18 are in the desiredlocation. The compliant body 12 and conduit 18 can then be removed andreplaced or exchanged as needed while the anchoring system remains inplace.

Referring now to FIGS. 12A and 12B, alternatively a permanentlyimplanted introducer or sheath 120 may be used to create a passage fromthe subcutaneous space outside the blood vessel, through the vessel walland to the desired site of device placement. The introducer 120 ispositioned during the initial procedure. Anchoring mechanisms may or maynot be attached to the introducer 120 to anchor it in a vessel in apatient and to anchor it in the pulmonary artery of a patient. Those ofskill in the art will appreciate that the introducer 120 may be shapedto a beneficial shape minimizing or removing the need for anchoringmechanisms. The compliant body 12 operably coupled to the transvascularconduit 28 may be passed through the introducer 120 and introduced intothe pulmonary artery with or without other guidance. This would allowfor easy replacement of the compliant body 12 as needed. If it is foundthat the compliant body and tranavascular conduit need to be removed,repositioned or exchanged they can be retracted or moved through thelumen (not shown) of the implanted introducer 120. Among other thingsthe implanted introducer prevents the transvascular conduit from beingencapsulated by the vascular wall as pace maker leads often are, offerssupport to the transvascular conduit and provides an anchoring platformthat may not need to be removed.

Referring to FIGS. 10D and 10B, the compliant body may alternatively bedesigned with integrated anchoring members 100 inherent in the shape ofthe compliant body. Anchoring members in the form of wings, fingers,fins, or like protuberances, may protrude from the surface or side ofthe compliant body 12 to center or wedge compliant body 12 in the vessel103. Exemplary embodiments of such anchoring members are depicted inFIGS. 10D and 10B at 102, 104, respectively.

Anchor members 100 may pass through the main pulmonary arterybifurcation FIG. 10B, contacting the distal vessel wall 103 beforebending back to touch the proximal vessel wall 104 downstream of thebifurication.

Alternatively, conduit 18 may be used to anchor the compliant body 12.Conduit 18 may be anchored in the right ventricle or proximate thepulmonary valve or valve annulus or the wall of the pulmonary artery. Itmay be anchored with transmural anchors, hooks, lead screw type anchorsor finger type entanglement anchors. The anchors may be removable andallow the conduit 18 and compliant body 12 to be easily removed.

Reservoir 14 may be free floating within a pocket in the tissue or maybe fastened in place with sutures and appropriate suture fixtures.

As will be appreciated by those of ordinary skill in the art, one ormore of the components of the device 10 may be implanted in anotherlocation without departing from the intended scope of the invention.Thus, the compliant body 12 and the reservoir 14 are described as beingimplanted in the pulmonary artery and the subcutaneous space beneath thesubclavicular skin, respectively, for purposes of example and notlimitation. Furthermore, the compliant body 12 may be implanted in thepulmonary artery via a pathway other than the subclavian vein withoutdeparting from the intended scope of the invention. Additionally, thedevice 10 of the invention may have use outside of reducing pulsatileload in an artery as will be appreciated by those of ordinary skill inthe art.

Pressure in the pulmonary artery varies with each heartbeat. When theheart contracts (systole) and ejects blood into the pulmonary artery,the pressure in the artery is relatively high. When the heart is filling(diastole) and in between beats, the pressure is relatively low. In anormal, healthy individual, the pulmonary artery is very compliant. Itselastic nature allows it to stretch to accommodate the incoming bloodwithout a large increase in pressure. In patients with pulmonaryarterial hypertension, for example, the artery walls are abnormallystiff. As a result, the heart must produce a higher pressure in order topump the same amount of blood into the pulmonary artery. Much like anormal pulmonary artery expands to make room for the incoming blood, thecompliant body 12 of the device 10 compresses to make room for the bloodbeing pumped through the pulmonary artery. This increases the complianceof the pulmonary artery and results in reduced systolic pressure in thepulmonary artery and right ventricle. The lower pressure reduces theworkload of the heart, ultimately preventing or delaying the formationof right heart failure, a leading cause of death in patients withpulmonary arterial hypertension.

The mechanical basis of the pressure reducing device of the inventionmay generally be represented by an accumulator. As appreciated by thoseof ordinary skill in the art, accumulators are pressure storagereservoirs that may be employed in plumbing systems to minimize pressurefluctuations in a pipe. FIGS. 2A and 2B are diagrams illustrating themechanical basis for the operation of the invention. Particularly, FIG.2A is a diagram illustrating a pulmonary artery having a low vascularcompliance, while FIG. 2B is a diagram of the same pulmonary artery witha means (i.e. the accumulator) for increasing the vascular compliance.With regard to FIG. 2A, during contraction of the heart the mitral valveis closed. Therefore, the predominant way blood ejected from the rightventricle may be accommodated is by expansion of the pulmonary artery.However, when the artery is “stiff” and has low compliance, there is alarge increase in arterial pressure due to the inelasticityc of theartery. Turning next to FIG. 2B, adding an accumulator to the lowcompliance artery of FIG. 2A results in an artery that once again has ahigh compliance. Specifically, although the artery itself is stillstiff, the gas-filled accumulator allows the volume in the artery tochange during systole with minimal change in pressure. Thus, the overallcompliance of the artery is increased even though the elasticity of theartery does not change.

Relating the foregoing discussion to the operation of the device 10,during systole the gas contained within the compliant body 12compresses. During diastole and between beats (when pressure in thepulmonary artery is relatively low) the gas in the compliant body 12expands. Consequently, the device 10 reduces the peak (systolic)pressure in the pulmonary artery and boosts the pressure in thepulmonary artery during diastole. By lowering the pressure when theheart is ejecting blood, and raising the pressure in the pulmonaryartery when the heart is not ejecting blood, the device reduces themechanical load on the right ventricle without adversely affecting bloodflow rate.

Now that the general structure and operation of the pressure reducingdevice 10 have been described, numerous design features of the variouscomponents will be set forth in detail. However, it should be understoodthat the particular components and their corresponding design featuresare described merely for purposes of example and not limitation. Thus,numerous other components and/or design features are contemplated andwithin the intended scope of the invention.

The compliant body 12 is a hollow, expandable vessel defined by an outermembrane that is structured for containing a compressible gas therein.The compliant body may be formed from elastic material (like a child'srubber balloon) or from a flexible but inelastic material (like themetalized mylar used in helium balloons). The balloon may be inflated sothe surface is taut or may be inflated slightly less so the surface isnot taut. The compliant body may also be multiple layers of multiplematerials with one or more layers being formed of composite materialswith reinforcing fibers. The compliant body 12 is preferably sized suchthat it may be positioned within the lumen of the pulmonary artery orother components of the cardiovascular system such as the aorta, rightor left atrium, or right or left ventricles. The entire compliant body12 may be located within the cardiovascular system or some or all of itmay be located outside the cardiovascular system. Furthermore, even whenpositioned completely within the cardiovascular system, the entirecompliant body 12 may be located in the lumen of a cardiovascular bodypart or it may extend into multiple lumina, such as in the lumen of theright ventricle and the lumen of the pulmonary artery or branches of thepulmonary artery.

The internal cavity of the compliant body 12 that is structured forholding the compressible gas is fluidly coupled to the lumen of thetransvascular conduit 18. In some embodiments, the compliant body 12 mayinclude more than one internal cavity. For example and referring toFIGS. 9A and 9B, in some embodiments a plurality of internal cavities93, 94 may exist in the compliant body 12 each with their own lumens 91,92, respectively, each fluidly coupled to the transvascular conduit 18,extravascular conduit 20, reservoir 14, port 16 and septum 22, as thecase may be. One or multiple cavities may be operated at differentpressures or volumes. One or multiple cavities may be dedicated to thedelivery of therapeutics through diffusion through the associated cavitymembranes 95, 96 or from direct orifices from the lumen to the blood.

As illustrated in FIG. 1, the shape of the compliant body 12 may be anelongated cylinder with tapered or rounded ends to reduce drag. Thelong, thin design of the compliant body 12 minimizes the cross-sectionalarea and resistance to flow caused by the device, and at the same timelowers PWV.

Although the compliant body 12 of FIG. 1 includes a generallycylindrical cross-sectional shape, numerous other cross-sectional shapesare also possible and within the intended scope of the invention asillustrated in FIG. 3. These cross-sectional shapes may be, for example,crescent shaped, cylindrical with cut-outs, fluted, oval, or the like.As will be appreciated by those of ordinary skill in the art, thecross-sectional shapes illustrated in FIG. 3 are provided merely forpurposes of example and not limitation. The compliant body 12 may be ofvarying cross sectional shape along its length. The compliant body mayhave a central lumen to accommodate a guide wire. The compliant body 12may be designed to equally distribute stress across the body and preventlocal stress concentrations. This may be achieved by forming the surfaceof the compliant body 12 from a series of radiuses 300 such as toprevent stress concentration in sharp corners. This principle may beapplied to any of the shapes in FIG. 3.

In other embodiments, the distal end of the compliant body 12 (oppositethe transvascular conduit attachment site) may be Y or T shaped, suchthat arms of the compliant body may be inserted into branches ofvessels. Embodiments having more than two arms are also contemplated.

The compliant body 12 may contain one or more sensors for monitoring oneor more physical properties of the cardiovascular system where it islocated, or alternatively for monitoring various parameters of thepressure reducing device 10. Examples of such properties and parametersinclude, but are not limited to, temperature, pressure, flow rate,oxygenation, CO₂ concentration, pH, luminal diameter, and the like.Markers may also be attached to or incorporated into the perimeter ofthe compliant body 12 for imaging as will be discussed in further detailbelow. As will be appreciated by those of ordinary skill in the art, thedevice 10 may have multiple independent lumens in the conduits 18, 20with multiple corresponding ports 16 and septums 22 in fluid connectionto multiple orifices located on or near the compliant body andtransvascular conduit 18 for the purpose of measuring commonhemnodynamic parameters. Referring to FIG. 13, the device may include aplurality of fluidly independent lumens 130, 130′ from the injectionport to the compliant body 12. These lumens may be of varying sizes andwith varying independent internal coatings and varying passages from thelumen to the interior of the compliant body. It may be beneficial tohave a lumen with a hydrophilic coating with a second lumen with ahydrophobic coating such that any absorbed and condensed water vaporenters the hydrophilic lumen and condenses. Dry gas can be introducedinto one of the lumens while water and moist gas can be drawn out theother. In this way the system can be purged and dried. The device may beconfigured with multiple lumens and one-way valves on one or multiplelumens such that gas flows to the compliant body through one lumen andreturns from the compliant body through another lumen. The return lumenmay pass through a liquid trapping device to trap condensed liquidacting as a desiccator-like trapping mechanism.

Referring to FIG. 14A, the device may have one or more openings 142,144, 146 from the lumen to the interior of the compliant body and theymay be arranged in a particular order radially around the lumen andalong the length of the compliant body to prevent them from beingblocked when the compliant body collapses.

Referring to FIG. 14B, the transvascular conduit 18 may pass through thecompliant body 12 and extend past 18′ the compliant body 12. The surfaceof the conduit 18 within the compliant body 12 may be coated withcompliant material or porous compliant material 140 which acts tocushion the surface of the conduit. Suitable materials may includepolymers, open cell foamed rubber, foamed rubber, silicones, woven orknitted fibers, dense brush-type materials such as Velcro and the like.Such coatings 140 will prevent acoustic pressure spikes in thesurrounding blood when the compliant body collapses completely.

Referring again to FIG. 12B the distal tip 18′ of the transvascularconduit may extend past the compliant body. Anchoring mechanisms may bemounted on this extended tip 18′, or the extended tip may follow thecurvature of the vasculature and assist in centering and curving thecompliant body so it follows the shape of the vessel.

The compliant body 12 is sized such that when it is inflated to thepredetermined pressure or volume, the cross sectional area that is takenup in the pulmonary artery is minimized as shown in FIG. 1. Inasmuch thecompliant body 12 is formed of a flexible material and its internal gasis compressible, during systole the systolic blood pressure will causethe compliant body 12 to contract to a contracted state, whereupon thevolume which it takes up within the pulmonary artery will be reduced.This contracting action has the effect of absorbing or reducing thesystolic pressure and also reducing the rate of change (i.e.acceleration) of blood flow.

During diastole the reduced diastolic pressure enables the gas withinthe compliant body 12 to expand to cause the compliant body 12 to assumeits expanded state again, thereby releasing the absorbed portion of thesystolic blood pressure. Thus, the repeated contracting and expandingaction of the compliant body 12 reduces the difference between peaksystolic pressure and diastolic pressure, all the while maintainingaverage blood pressure and blood flow. Consequently, cardiac workload isreduced without a concomitant reduction in cardiac output.

The volumetric capacity of the compliant body 12 is selected such thatit can collapse to absorb enough of the ventricular ejection volume tosignificantly lessen peak systolic pressure. Since the heart of an adulttypically ejects 2-6 liters per minute, the ejection or stroke volumeper contraction of the heart will generally be between 25-100 ml(assuming a pulse rate range of 60-80 beats per minute), with mostpatients having a stroke volume of about 60 ml. In order to meaningfullyreduce the systolic pressure of such persons, it is contemplated thatthe compliant body 12 should have a volumetric capacity so that when itis in the expanded state during diastole it displaces at least about 5ml of blood volume within the pulmonary artery (for pediatricapplications the volumetric, capacity may be less, such as about 1 or 2mil). In order to achieve this result, in one exemplary embodiment thepressure reducing device 10 is injected with between about 60 and about1000 ml of gas (distributed between the compliant body 12 and thereservoir 14). Accordingly, when the compliant body 12 is compressed bysystolic pressure it can affect a significant reduction in systolicpressure. Compliant bodies with larger capacities may be used to provideeven greater reductions in the systolic pressure so long as they aresuitable for disposition within the vascular system.

As will be appreciated by those of ordinary skill in the art, anysuitable biocompatible gas may be used in the pressure reducing device10. In one exemplary embodiment, the gas is a compressible gas such thatits volume changes in response to a change in pressure in the artery (orother implantation location of the compliant body 12) consistent withthe gas bulk modulus of the gas. Furthermore, the gas is preferablynontoxic, easily absorbed by the body, and has physical properties thatresist diffusion through the compliant body membrane. Suitable gases mayinclude, but are not limited to, nitrogen and carbon dioxide.Optionally, the gas may have therapeutic properties, such as nitricoxide which causes vasodilation.

The membrane of the compliant body 12 that encapsulates the volume ofgas may be formed from a thin, sheet-like structure comprising one ormore materials or layers. As will be appreciated by those of ordinaryskill in the art, any suitable material that is both biocompatible andflexible may be used that enables pressure changes external to thecompliant body to be transmitted to the gas. The use of a biocompatiblematerial is important to enable the compliant body 12 to perform itsfunction in the body without eliciting an undesirable local or systemicresponse. In order to preserve the injected volume of gas within thepressure reducing device 10, a membrane material that minimizesdiffusion of gas through the membrane may be preferable. Additionally,the membrane may be elastic, such that the compliant body 12 can returnto its original shape after deformation, and resistant to fatigue, suchthat the compliant body 12 maintains its strength and integrity aftermultiple deformations.

In order to prevent thrombus formation after implantation, the membraneis preferably antithrombotic. As will be appreciated by those skilled inthe art, the membrane surface may be biomimetic or have inherentantithrombotic properties or its external surface may be coated with amaterial to prevent thrombus formation, such as heparin or the like.Additionally, the membrane may be lubricious, such that it impedesadhesion of body components such as platelets, proteins, endothelium,endocardium, or heart valves. Any suitable biocompatible lubricant maybe used including, but not limited to, silicone or hyaluronan basedmaterials. The shape of the membrane may also be carefully defined toeliminate dead space in the surrounding blood flow to minimize thrombusformation.

In some embodiments, it may be preferable to select a membrane materialthat is MRI compatible. Radio-opaque or other markers may beincorporated or attached to the compliant body 12 for imaging. The useof such marker elements allows for viewing of the compliant body with asuitable imaging system, such as x-ray, MRI scanner or fluoroscopicsystem. As will be appreciated by those skilled in the art, any suitablemarker elements and imaging system may be used without departing fromthe intended scope of the invention.

Turning next to the reservoir 14, this component resembles a hollow,thin-walled vessel that is structured for receiving the compressible gastherein. The reservoir 14 is preferably sized such that it may bepositioned within the subcutaneous space in the region of the right orleft subclavian veins. However, the reservoir 14 may be positionedwithin any suitable body cavity having sufficient space withoutdeparting from the intended scope of the invention. Although anysuitable shape may be used, in one exemplary embodiment the reservoir 14may be a rounded, flattened disk to minimize protrusion through thepatient's skin.

The interior cavity of the reservoir 14 is in fluid communication withthe interior cavity of the compliant body 12 via a lumen of thetransvascular conduit 18 such that gas may move between the cavitiesand/or pressure may equalize between the cavities. The interior cavityof the reservoir 14 is also in fluid communication with the injectionport 16 via a lumen of the extravascular conduit 20 such that gas maymove between the reservoir 14 and the injection port 16 and/or pressuremay equalize between them.

As will be appreciated by those of ordinary skill in the art, thereservoir 14 may be formed from any suitable material or materials thatprevent or minimize diffusion of the gas from the internal cavitythrough the outer walls. However, the material must be biocompatiblesuch that it is able to perform its function in the body withouteliciting an undesirable local or systemic response. Similar to thecompliant body 12, the reservoir material may also be MRI compatible.Radio-opaque or other markers may be incorporated into the perimeter ofthe reservoir 14 for imaging. The use of such marker elements allows forviewing of the reservoir with a suitable imaging system.

Optionally, the external surface of the reservoir 14 may be lubricious,such that it impedes adhesion of body components such as platelets orproteins. Exemplary but not limiting lubricants may include silicone orhyaluronan based materials.

The reservoir 14 may contain one or more sensors for monitoring one ormore parameters of the pressure reducing device 10. Examples of suchparameters include, but are not limited to, the gas pressure or volumewithin the reservoir 14. As appreciated by those of ordinary skill inthe art, such measurements may be used to determine when filling of thereservoir is required.

In some embodiments, the reservoir 14 may contain electrical leads andcouplings for transmitting signals to and from the compliant body 12and/or the injection port 16. The reservoir 14 may also contain atransmitter and receiver for sending and receiving telemetric signalsto/from an external station. For example, the signals may be used totransmit the properties or parameters monitored by the reservoir 14and/or compliant body 12, such as volume, pressure, temperature, flowrate, oxygenation, CO₂ concentration, pH, luminal diameter, or the like.Additionally, the reservoir 14 may include a data storage means forstoring data that may be interrogated and uploaded at a later time. Oneof the parameters measured may be reservoir pressure to assist in properfilling and monitoring of the system. For example, if it is found thatthe reservoir pressure remains constant, one can infer that thecompliant body is collapsed or if the pressure is constant for someportion of the cardiac cycle then the balloon is collapsing completely,and needs to be inflated by some volumetric amount until the waveformhas no flat sections.

The injection port 16 is structured and operable to allow the additionof gas to or the removal of gas from the reservoir 14. The interiorcavity of the injection port 16 is in fluid communication with thereservoir 14 via a lumen of the extravascular conduit 20 such that gasmay move freely between the cavities and/or pressure may equalizebetween the cavities. Optionally, one or more valves may be used toassist with controlling the flow of gas to the reservoir 14. Uponimplantation of the pressure reducing device 10, the injection port 16may be disposed wholly underneath the patient's skin or alternativelymay pass through the patient's skin to provide an exposed portionexternal to the patient's body.

In one exemplary alternative embodiment, the injection port 16 may bemounted directly on the reservoir 14 instead of fluidly coupling theport to the reservoir with the extravascular conduit 20. However, such adesign eliminates a surgeon's option of locating the injection port 16external to the patient's body.

Similar to the compliant body 12 and the reservoir 14, the injectionport 16 may be formed from any suitable material or materials thatprevent or minimize diffusion of the gas from the internal cavity of theport and through the outer walls. However, the material must bebiocompatible such that it is able to perform its function in the bodywithout eliciting an undesirable local or systemic response. Thereservoir material is also preferably lubricious and MRI compatible.Radio-opaque or other markers may also be incorporated into or attachedto the injection port 16 to allow for viewing or tracking of theinjection port with a suitable imaging system.

As illustrated in FIG. 1, the injection port 16 may include a septum 22that allows for repeated needle penetrations while maintaining agas-tight seal. Any suitable septum design may be used that provides agas-tight seal. Exemplary injection ports that may be suitable for usein the pressure reducing device 10 of the invention include the SmartPort®, LifePort®, TitanPort®, Triumph-1®, and Vortex® Ports fromAngioDynamicsInc., and the PowerPort®, SlimPort®, X-Port®, and variousother M.R.I. compatible ports from C. R. Bard, Inc. The injection port16 may also be a mechanical structure suitable for direct connection toa syringe for pressure or volume adjustments or a therapeutic gas orliquid supply. The mechanical structure may have internal valves and orelectrical contacts.

In embodiments such as that illustrated in FIG. 1 where the injectionport 16 is not mounted directly to the reservoir 14 and instead includesthe extravascular conduit 20, the conduit is structured for positioningin the subcutaneous space or body cavity adjacent to the reservoir 14and provides for fluid communication between the components. Theextravascular conduit 20 is structured as a thin elongated cylinder witha lumen that allows for conveyance of gas to the reservoir 14.Optionally, the extravascular conduit 20 may include multiple lumensthat provide multiple gas lines, or alternatively a first lumen for gasand one or more additional lumens for electrical leads, transmissionlines, or the like for transmitting electrical signals between thereservoir 14 and the injection port 16.

The extravascular conduit 20 may be formed from any suitable material ormaterials that prevent or minimize diffusion of the gas from the lumenor lumens of the conduit. However, the material must be biocompatiblesuch that it is able to perform its function in the body withouteliciting an undesirable local or systemic response. The extravascularconduit 20 may be formed from a material that is lubricious, as well asflexible to allow the conduit to move freely within the subcutaneousspace or body cavity. The extravascular conduit 20 may also be formedfrom a material that is MRI-compatible and fatigue resistant such thatit maintains its strength and integrity after multiple deformations.

As will be appreciated by those of ordinary skill in the art, it may beimportant to monitor or track the position of the extravascular conduit20 after implantation to ensure that the conduit has not moved to anundesirable location. To that end, radio-opaque or other markers may bepositioned at discrete intervals along the length of the conduit.

The extravascular conduit 20 may be coupled to the reservoir 14 and theinjection port 16 in any suitable manner including, but not limited to,heat welding, a compression fit, or with a biocompatible adhesive.

Finally, the transvascular conduit 18 may be structured as a thinelongated cylinder with a lumen that allows for conveyance of gas and/orequalization of pressure between the reservoir 14 and the compliant body12. As illustrated in FIG. 1, the proximal end of the transvascularconduit 18 is connected to the reservoir 14. Moving distally away fromthe reservoir 14, the transvascular conduit 18 starts in thesubcutaneous space inferior to the subclavian vein, enters thesubclavian vein, passes through the superior vena cava, right atrium,tricuspid valve, right ventricle, and the pulmonary valve, and thenenters the pulmonary artery where it connects to the compliant body 12at its distal end.

As illustrated in FIG. 1, the transvascular conduit 18 may be whollycontained in the lumen of a cardiovascular component. However, inalternative embodiments, the transvascular conduit 18 may pass throughthe wall of a cardiovascular component such that part of the conduit isin the lumen of a cardiovascular component and part of the conduit isoutside the cardiovascular component.

The transvascular conduit 18 may be formed from a biocompatible materialthat prevents or minimizes diffusion of the gas from the lumen. Thetransvascular conduit 18 is also preferably flexible so as to allow theconduit to move freely with adjacent body motions such as heartcontractions and fatigue resistant such that it maintains its strengthand integrity after multiple deformations. In order to impede adhesionof body components and allow for easier insertion through thevasculature, the external surface of the conduit may be lubricious.

Because the transvascular conduit 18 is guided through the patient'svasculature and is therefore not visible by the human eye, it may bedesirable to monitor or track the position of the conduit after and/orduring implantation. To that end, one or more radio-opaque markers maybe incorporated into the wall or positioned at discrete intervals alongthe length of the transvascular conduit 18 to monitor the location ofthe conduit and ensure that it is positioned properly within thepatient.

The transvascular conduit 18 may be coupled to the compliant body 12 andthe reservoir 14 in any suitable manner including, but not limited to,heat welding, a compression fit, or with a biocompatible adhesive.Furthermore, connection of the components may also incorporate the useof one or more valve elements. In one exemplary embodiment, a firsttwo-way valve is positioned at the interface between the compliant body12 and the distal and of the transvascular conduit 18 and a secondtwo-way valve is positioned at the interface between the reservoir 14and the proximal end of the transvascular conduit 18.

Optionally, the transvascular conduit 18 may include multiple lumensthat provide for multiple gas lines, or alternatively a first lumen forgas and one or more additional lumens for electrical leads, transmissionlines, or the like for transmitting electrical signals between thereservoir 14 and the compliant body 12. The transvascular conduit 18 maycontain a lumen for a guide wire to assist placement or removal of thedevice 10. Additionally, the transvascular conduit 18 may include one ormore sensors for monitoring physical properties of the cardiovascularsystem and/or device parameters as discussed above with regard to theother device components. The transvascular conduit may be of varyingcross sectional profile and area along its length.

FIG. 4 is a diagram illustrating a “bench top” pulmonary circulationtest apparatus 24 used to simulate the operation of the pulmonaryvasculature and test various pressure reducing devices in accordancewith the invention to verify their operability. As illustrated in FIG.4, the pulmonary circulation test apparatus 24 is a closed loop circuitthat is tuned to match human hemodynamic characteristics of thepulmonary artery. Particularly, the test apparatus 24 includes a chamber25 operably coupled to a piston pump 26 for simulating the functionalityof the right ventricle. The chamber 24 includes a first mechanical valve27 on an input side simulating the operation of the tricuspid valve anda second mechanical valve 28 on an output side simulating the operationof the pulmonary valve. A first air filled chamber 29 is operablycoupled to the chamber for adjusting the “ventricular compliance.” Thepulmonary artery is simulated in the test apparatus by a first pressuresensor 30, a second pressure sensor 31, a flow meter 32, and a secondair filled chamber 33 for adjusting the “arterial compliance.”Downstream of the “pulmonary artery components,” a bifurcation element34 and a needle valve 35 simulate the operation of the right and leftpulmonary arteries, and a fluid reservoir 36 serves as the source offluid that is circulated through the test apparatus 24. The fluidreservoir 36 has a capillary wedge pressure 37 that is adjustable.

The particular fluid circulated through the test apparatus was 0.9%saline. Stroke volume, heart rate, mean and pulsatile pressure (mm Hg),flow rate (L/min.), pulmonary vascular resistance (Woods Units),capillary wedge pressure (mm Hg), and compliance of the right ventricleand pulmonary artery were set to match hemodynamic parameters obtainedfrom traces of right heart catheterization procedures from patients withand without pulmonary arterial hypertension. Particularly, thehemodynamic parameters of a typical patient were found to be accuratelyrepresented in the test apparatus by a stroke volume of from 30 to 80 mlheart rate of 50 to 100 beats per minute, mean and pulsatile pressure offrom 12 to 60 and 10 to 60 mmHg, cardiac output of from 2 to 8 litersper minute, and capillary wedge pressure of from 5 to 20 mmHg.

In order to evaluate the performance of the pressure reducing device ofthe invention, pressure and flow data were obtained with the devicepresent and absent. When present, the pressure reducing device wasoperably positioned within the test apparatus 24 at a device location 38between the first pressure sensor 30 and the second pressure sensor 31.

FIG. 5 is a graph illustrating the exemplary effect of the pressurereducing device on peak pressure that was achieved using the testapparatus 24. Particularly, the graph tracks changes in pressure duringsystole and diastole. The first curve P1 represents pressure in a lowcompliance artery with the device 10 “turned off,” while the secondcurve P2 represents pressure in a low compliance artery with the device10 “turned on.” As illustrated in FIG. 5, the test apparatusdemonstrates an approximately 15% reduction in peak pressure when thepressure reducing device is activated. The graph of FIG. 5 also showshow the pressure reducing device causes the pressure to be slightlyelevated during diastole, thus having minimal impact on mean pulmonarypressure.

FIGS. 6A and 6B are diagrams illustrating a first alternative embodimentof a pressure reducing device 10 in accordance with the invention. Thedevice 10 is generally similar to the device 10 previously described,and includes a compliant body 12 fluidly coupled to a reservoir 14 by atranavascular conduit 18. Although not illustrated, the device 10 mayalso include an injection port and an extravascular conduit aspreviously described. However, unlike the pressure reducing device 10,both the compliant body 12 and the reservoir 14 of the device 10 areformed from an elastic material. Additionally, the device 10 may befilled with either a compressible gas (as discussed in detail above) ora non-compressible fluid (of any state). As will be appreciated by thoseof ordinary skill in the art, any fluid that is both non-compressibleand biocompatible may be used, such as a saline solution.

As illustrated in FIG. 6A, during systole(P_(PulmonaryArtery)>P_(Reservoir)), high pressure in the pulmonaryartery causes the gas/fluid to move out of the compliant body 12 andinto the reservoir 14. The elasticity of the reservoir walls allows thereservoir 14 to stretch and accommodate an increased volume. Conversely,during diastole (P_(PulmonaryArtery)>P_(Reservoir)), the elastic forcesof the walls of the reservoir 14 move the gas/fluid back into thecompliant body 12 as illustrated in FIG. 6B, thus increasing the volumeof the compliant body 12. As will be appreciated by those of ordinaryskill in the art, the net effect of the movement of gas/fluid betweenthe compliant body 12 and the reservoir 14 is to reduce systolicpressure and boost diastolic pressure in the pulmonary artery. In thisembodiment, the compliance in the pulmonary artery is increased duringsystole primarily by stretching of the reservoir's elastic walls ratherthan compression of the gas in the compliant body.

One benefit of using a non-compressible fluid in place of a compressiblegas may be less need for refilling the device 10 after implantation.Additionally, a non-compressible fluid may allow for better control whenused in an active system as will be described below with reference toFIG. 7. Numerous other benefits are inherent to the use of anon-compressible fluid as will be appreciated by those of ordinary skillin the art.

FIG. 7 is a diagram illustrating a second alternative embodiment of apressure reducing device 10B in accordance with the invention. Thedevice 10B may be generally similar to either the device 10 or thedevice 10A previously described, and includes a compliant body 12B, areservoir 14B, an injection port 16B, a transvascular conduit 18Bfluidly coupling the compliant body 12B to the reservoir 14B, and anextravascular conduit 20B fluidly coupling the reservoir 14B to theinjection port 16B. However, as illustrated in FIG. 7, the pressurereducing device 10B further includes a controllable pulsatile pump 40that allows for active control of the inflation/deflation of thecompliant body 12B. Any suitable pump that is operable to control themovement of fluid within the pressure reducing device 10B may be used asthose of ordinary skill in the art will appreciate. In one exemplaryembodiment as illustrated in FIG. 7, the pulsatile pump 40 may include alinear actuator 42 that is operable to precisely control the linearmovement of a piston 44 to inject fluid into and extract fluid from thecompliant body 12B.

Particularly, the device 10 may function as an open or closed loopcontrol system that is operable to minimize cardiac work whilemaintaining cardiac output. In one exemplary embodiment, the device 10may be operable to increase compliance in the pulmonary artery bydecreasing the volume in the compliant body 12 during systole andincreasing the volume in the compliant body 12 during diastole. As willbe appreciated by those of ordinary skill in the art, the overall effectis to decrease systolic pressure and increase the pressure duringdiastole and between beats.

The pulsatile pump 40 may be a permanent part of the device 10, or itmay be operably coupled to the device 10 for short-term use. This wouldallow the pressure reducing device 10 to adapt to patient needs byadding the functionality of an active system whenever necessary, such asfor emergency therapy or as the disease progresses.

A suitable control means such as a CPU 46 may be operably coupled to thepulsatile pump 40 for controlling operation of the pump. The CPU 46 mayreceive input signals from one or more sensors or monitoring devices,such as a pressure sensor 48 operably coupled to the compliant body 12and an ECO 50 operably coupled to the patient. However, sensors may beprovided that monitor numerous other types of parameters or properties.Additionally, the CPU 46 may be operably coupled to an input means toallow for the manual input of control commands by the attendingphysician.

The foregoing alternative embodiments were described merely for purposesof example and not limitation. As will be appreciated by those ofordinary skill in the art, the pressure reducing devices of theinvention may be provided with numerous other design features andfunctionalities. In another alternative embodiment, the pressurereducing device may include a lumen for delivering one or more drugs toa patient. The drugs may work together with the pressure reducing deviceto relieve the effects of pulmonary arterial hypertension. In anotheralternative embodiment, the transvascular conduit may carry one or moreelectrical leads for a pacemaker device that helps control abnormalheart rhythms. Alternatively, the conduit itself may contain electricalconduction properties so that it may function as a lead for a pacemaker.The pacemaker device that is operably coupled to the leads may beincorporated into the pressure reducing device of the invention, such asbeing attached to or positioned within the reservoir. Alternatively, thepacemaker device may be a stand-alone unit that is implanted separatelyfrom the reservoir. In yet another alternative embodiment, the pressurereducing device of the invention may include a pressure relief means forrelieving the build-up of pressure within the device to prevent damageto the device and/or physical harm to the patient. For example, thepressure relief means may comprise a pressure relief valve associatedwith one or more components of the device, such as the reservoir, thatis designed to open at a predetermined set pressure to protect thedevice from being subjected to pressures that exceed its design limits.

As will be appreciated by those of ordinary skill in the art based onthe foregoing, the invention provides numerous benefits and advantagesover previous designs. The pressure reducing device of the invention maybe implanted in a minimally invasive procedure that does not requiregeneral anesthesia. This is an important factor for patients withadvanced cardio respiratory compromise, as occurs with pulmonaryarterial hypertension. Furthermore, the implantation procedure may beperformed by a physician with minimal surgical skill such as aninterventional radiologist, interventional cardiologist, or acardiologist. Not only is the device of the invention easilyimplantable, but it is also removable.

In one embodiment, the pressure reducing device of the invention may bepassive and therefore would not require an external energy source. Itwould also address the problem of filling the device upon initialimplantation and keeping the device inflated over time. Particularly,the device provides remote access via the injection port which allowsthe compliant body to be queried and adjusted to a desired inflationlevel. Thus, the device does not require a transvascular procedure tofill and does not require an access line to cross an arterial wall.

Although passive devices are simpler and well-suited for long term use,active embodiments, as disclosed herein, are also contemplated andwithin the scope of the invention. Active device are suited forsituations that require more control, such as for emergency therapy orwhen the disease progresses.

The long compliant body of the pressure reducing device is designed toslow the PWV (i.e. minimize the effect of reflected waves on pulsepressure). Particularly, the long, thin shape of the compliant bodyminimizes the cross-sectional area of the artery that is taken up by thedevice. Consequently, the resistance to flow caused by the presence ofthe compliant body in the artery is minimized (i.e. minimalintra-arterial volume means minimum flow restriction caused by thedevice).

As will be appreciated by those of ordinary skill in the art, providinga long, thin compliant body in combination with a large extravascularreservoir located remote from the pulmonary artery increases vascularcompliance due to the fact that much of the fluid volume is locatedoutside of the artery. As will further be appreciated by those ofordinary skill in the art, a large reservoir volume translates to betterperformance with respect to pressure reduction.

Another benefit of the invention is the capability of monitoring one ormore physical properties of the cardiovascular system and/or one or moreparameters of the pressure reducing device. The monitoring may beperformed using any suitable sensor operably coupled to the reservoir,compliant body, injection port, extravascular conduit, or transvascularconduit. The monitored properties or parameters may include temperature,pressure, flow rate, oxygenation, CO₂ concentration, pH, luminaldiameter, or the like.

In addition to providing components that assist with the reduction ofpressure within the cardiovascular system, the device of the inventionmay also include components that assist with the delivery of one or moredrugs. In one exemplary embodiment, the device may be operable todeliver a drug for treating pulmonary arterial hypertension, such asIloprost.

FIG. 8 is a flowchart diagram illustrating exemplary but non-limitingtherapeutic pathways associated with the pressure reducing device of theinvention. In summary, by increasing the compliance of the pulmonaryartery the device of the invention is able to (I) slow the progressionof small vessel disease, (II) increase cardiac output, and (III) preventor delay the onset of right heart failure.

Although the invention has been described with reference to preferredembodiments, workers skilled in the art will recognize that changes maybe made in form and detail without departing from the spirit and scopeof the invention.

1-43. (canceled)
 44. A system for reducing pulsatile arterial elastanceand increasing pulsatile arterial compliance, comprising: a fluidreservoir having a housing, said housing defining a unitary fluidchamber within said reservoir, an injection port fluidly connected tosaid fluid reservoir, said injection port being separate from said fluidreservoir or mounted directly on said fluid reservoir; a transvascularconduit; and a compliant body that is compressible and generallyelastic, defines an internal volume, and is configured to be placedfreely within a vascular lumen of a patient, characterized in that saidinternal volume of said compliant body is capable of responsivelychanging when subjected to changing pressure within the vascular lumen,and the transvascular conduit fluidly connects said fluid reservoir andsaid compliant body.
 45. The system of claim 44, wherein said fluidreservoir is configured to be implanted subclavically in the patient;said injection port is configured to be implanted subcutaneously in thepatient; and said compliant body and said transvascular conduit are bothconfigured to be intraluminally delivered and placed in the patient. 46.The system of claim 44, wherein said compliant body is operable tocontract during systole and expand during diastole.
 47. The system ofclaim 44, wherein the fluid is a compressible fluid or wherein the fluidis a non-compressible fluid, optionally further comprising anextravascular conduit extending between and fluidly coupling theinjection port and the reservoir.
 48. The system of claim 44, whereinthe compliant body includes an outer membrane formed from a materialselected from an elastic material and an inelastic material, for examplewherein the inelastic material is a flexible material.
 49. The system ofclaim 48, wherein the compliant body has a circular shapedcross-section, or wherein the compliant body has an oval shapedcross-section, or wherein the compliant body has a crescent shapedcross-section, and/or wherein the compliant body is shaped as anelongated cylinder having rounded distal and proximal ends.
 50. Thesystem of claim 44, further comprising a pump operably coupled to theinjection port for controlling a fluid volume of the compliant body,preferably further comprising a processor unit operably coupled to thepump for controlling operation of the pump.
 51. The system of claim 44,further comprising one or more sensors for monitoring one or moreparameters, for example wherein the parameter is fluid volume within thecompliant body, or wherein the parameter is pressure within thereservoir.
 52. The system of claim 44, wherein the compliant bodyincludes a plurality of lumens each of which is fluidly coupled to thetransvascular conduit, extravascular conduit, and reservoir and/orfurther comprising an anchoring member for anchoring the compliant bodyin said lumen, preferably wherein said anchoring member is operablycoupled to an outer surface of said compliant member, for examplewherein said anchoring member is structured to expand radially outwardto contact the vessel lumen, or wherein said anchoring member isreceived within said at least one compliant body lumen and structured toexpand radially through said compliant body to contact said vessel. 53.The system of claim 44, further comprising a sheath surrounding saidcompliant body and said transvascular conduit, optionally furthercomprising an anchoring member structured to expand radially outward tocontact the vessel wall when said sheath is retracted.
 54. The system ofclaim 44, wherein said transvascular conduit comprises an anchoringmember structured to anchor said complaint body in said vessel lumen byanchors selected from transmural anchors, lead screw anchors and fingertype entanglement anchors and/or further comprising a sheath having alumen, said sheath configured to be anchored in a pulmonary artery of apatient to accommodate the delivery and removal of said compliant bodyoperably coupled to said transvascular conduit through said sheathlumen.
 55. The system of claim 44, wherein said transvascular conduitextends into an interior of said compliant body, optionally wherein asurface of the transvascular conduit extending into the compliant bodyincludes a coating selected from the group consisting of a compliantmaterial, a porous compliant material, and combinations of theforegoing, optionally further comprising one or more openings on saidtransvascular conduit fluidly coupling the lumen of said transvascularconduit and the interior of said compliant body.
 56. The system of claim44, wherein said transvascular conduit includes a plurality of fluidlyindependent lumens, each of said lumens in fluid communication with saidinjection port and an interior of said compliant body, for examplewherein at least one of said plurality of lumens has a hydrophiliccoating and at least a second of said plurality of lumens has ahydrophobic coating such that an absorbed and condensed water vapor thatenters the lumen with the hydrophilic coating condenses.
 57. The systemof claim 56, further including a liquid trapping device operably coupledto a return lumen, and/or wherein one or more of said plurality oflumens includes a one-way valve, or wherein one or more of saidplurality of fluidly independent lumens terminate proximal or distal tothe compliant body, for example wherein said one or more of saidplurality of fluidly independent lumens are configured to convey adiagnostic or therapeutic agent.
 58. The system of claim 44, wherein thecompliant body is structured to be implanted in the lumen of thepatient's pulmonary artery for treating pulmonary arterial hypertension.59. A system for reducing pulsatile pressure comprising: a reservoirstructured to be implanted subcutaneously, said reservoir for holding afluid therewithin; an injection port in fluid communication with thereservoir, a transvascular conduit; and a compliant body structured tobe implanted in a lumen of a vessel, said compliant body including atleast one compliant body lumen, characterized in that said compliantbody is structured for expansion and compression upon changes inpressure in the vessel, the transvascular conduit extends between andfluidly couples the reservoir and said at least one compliant bodylumen, and said compression of the compliant body results in a reductionin peak pressure in the vessel.
 60. The system of claim 59, wherein saidcompliant body is operable to contact during systole and expand duringdiastole.
 61. The system of claim 59, wherein the fluid is acompressible fluid or wherein the fluid is a non-compressible fluid,optionally further comprising an extravascular conduit extending betweenand fluidly coupling the injection port and the reservoir.
 62. Thesystem of claim 59, wherein the compliant body includes an outermembrane formed from a material selected from an elastic material and aninelastic material, for example wherein the inelastic material is aflexible material.
 63. The system of claim 62, wherein the compliantbody has a circular shaped cross-section, or wherein the compliant bodyhas an oval shaped cross-section, or wherein the compliant body has acrescent shaped cross-section, and/or wherein the compliant body isshaped as an elongated cylinder having rounded distal and proximal ends.64. The system of claim 59, further comprising a pump operably coupledto the injection port for controlling a fluid volume of the compliantbody, preferably further comprising a processor unit operably coupled tothe pump for controlling operation of the pump.
 65. The system of claim59, further comprising one or more sensors for monitoring one or moreparameters, for example wherein the parameter is fluid volume within thecompliant body, or wherein the parameter is pressure within thereservoir.
 66. The system of claim 59, wherein the compliant bodyincludes a plurality of lumens each of which is fluidly coupled to thetransvascular conduit, extravascular conduit, and reservoir and/orfurther comprising an anchoring member for anchoring the compliant bodyin said lumen, preferably wherein said anchoring member is operablycoupled to an outer surface of said compliant member, for examplewherein said anchoring member is structured to expand radially outwardto contact the vessel lumen, or wherein said anchoring member isreceived within said at least one compliant body lumen and structured toexpand radially through said compliant body to contact said vessel. 67.The system of claim 59, further comprising a sheath surrounding saidcompliant body and said transvascular conduit, optionally furthercomprising an anchoring member structured to expand radially outward tocontact the vessel wall when said sheath is retracted.
 68. The system ofclaim 59, wherein said transvascular conduit comprises an anchoringmember structured to anchor said complaint body in said vessel lumen byanchors selected from transmural anchors, lead screw anchors and fingertype entanglement anchors and/or further comprising a sheath having alumen, said sheath configured to be anchored in a pulmonary artery of apatient to accommodate the delivery and removal of said compliant bodyoperably coupled to said transvascular conduit through said sheathlumen.
 69. The system of claim 59, wherein said transvascular conduitextends into an interior of said compliant body, optionally wherein asurface of the transvascular conduit extending into the compliant bodyincludes a coating selected from the group consisting of a compliantmaterial, a porous compliant material, and combinations of theforegoing, optionally further comprising one or more openings on saidtransvascular conduit fluidly coupling the lumen of said transvascularconduit and the interior of said compliant body.
 70. The system of claim59, wherein said transvascular conduit includes a plurality of fluidlyindependent lumens, each of said lumens in fluid communication with saidinjection port and an interior of said compliant body, for examplewherein at least one of said plurality of lumens has a hydrophiliccoating and at least a second of said plurality of lumens has ahydrophobic coating such that an absorbed and condensed water vapor thatenters the lumen with the hydrophilic coating condenses.
 71. The systemof claim 70, further including a liquid trapping device operably coupledto a return lumen, and/or wherein one or more of said plurality oflumens includes a one-way valve, or wherein one or more of saidplurality of fluidly independent lumens terminate proximal or distal tothe compliant body, for example wherein said one or more of saidplurality of fluidly independent lumens are configured to convey adiagnostic or therapeutic agent.
 72. The system of claim 59, wherein thecompliant body is structured to be implanted in the lumen of thepatient's pulmonary artery for treating pulmonary arterial hypertension.